1. Field of the Invention
The present invention relates to integrated circuit packaging technology.
2. Background Art
Integrated circuit (IC) chips or dies from semiconductor wafers are typically interfaced with other circuits using a package that can be attached to a printed circuit board (PCB). One such type of IC package is a ball grid array (BGA) package. BGA packages provide for smaller footprints than many other package solutions available today. A BGA package includes a die attached to substrate of the package, and an array of solder ball pads located on a bottom external surface of the package substrate. Solder balls are attached to the solder ball pads. The solder balls are reflowed to attach the package to the PCB.
In some BGA packages, signals of the die are interfaced with electrical features (e.g., bond fingers) of the substrate using wire bonds. In such a BGA package, wire bonds are connected between signal pads/terminals of the die and electrical features of the substrate. In another type of BGA package, which may be referred to as a “flip chip package,” a die may be attached to the substrate of the package in a “flip chip” orientation. In such a BGA package, solder bumps are formed on the signal pads/terminals of the die, and the die is inverted (“flipped”) and attached to the substrate by reflowing the solder bumps so that they attach to corresponding pads on the surface of the substrate.
Typically IC packages are asymmetrical (in the direction perpendicular to the plane of the substrate), and are mechanically unbalanced. This asymmetry, along with the different materials used in the packaging (e.g., an organic package substrate, which has a different coefficient of thermal expansion (CTE) than the IC die), cause both mechanical and thermal stresses, which in turn lead to package warpage and co-planarity issues. Package warp can place stress on the solder joints of the die, leading to detachment of some of the solder bumps and/or physical damage to the die. Thus, flip chip packages are frequently configured to disperse the generated heat, such as though the inclusion of heat sinks. For instance, a heat spreader in the form of a cap may be mounted to a package over the die to aid in dispersing excess heat and to reducing package warping. The die may be interfaced with the heat spreader by an adhesive that conducts heat from the die to the heat spreader. However, properties of the adhesive material determine whether the adhesive is more effective at transferring heat from the die to the heat spreader, or is more effective at adhering to the heat spreader in a manner that enhances package strength and thereby reduces package warping. Current adhesive materials tend to be effective at heat transfer or at warp prevention, but are not highly effective at both.